This paper presents a detailed empirical description of airport connectivities in four major multiple airport cities (London, New York, Los Angeles, and San Francisco). Our analysis draws on data derived from a previously largely untapped information source, i.e. the so-called Marketing Information Data Transfer (MIDT). This dataset contains information on actually flown transnational routes, which allows for a thorough assessment of the chief connectivity characteristics of specific airports. Combined with information derived from a number of other sources, our results point to functional divisions among airports, both in terms of their geographical scale (e.g. national, regional, and international airports) and their specific role in the airline network (e.g. origin/destination versus hub airports). The implications of the results are discussed, and some avenues for future research are considered.